Contemporary vehicle engines are equipped with exhaust-gas aftertreatment devices, which serve to convert harmful exhaust-gas pollutants (e.g., NOx, CO, hydrocarbons, and the like) to inert or environmentally benign gases such as water vapor and nitrogen, thereby preventing their release into the environment. Some examples of such exhaust-gas aftertreatment devices include diesel particulate filters (DPF), diesel oxidation catalyst (DOC), lean NOx traps (LNT), and selective catalyst reduction devices (SCR). However, exhaust-gas aftertreatment devices exhibit high conversion efficiency within a relatively narrow temperature window, the temperature window being dependent, for example, on the metal substrate or type of catalyst used. When pollutant-containing exhaust-gases flow through exhaust-gas aftertreatment devices whose operating temperature is outside of the optimal temperature window, conversion efficiency is low and environmentally harmful pollutants are emitted from the vehicle. For example, DOC temperatures can be below light-off temperatures for oxidizing pollutants such as exhaust hydrocarbons during a period following cold engine starts. For this reason, post-injection of fuel is often used to heat up the exhaust-gas when the exhaust-gas temperature is low. An alternate approach incorporates a pre-turbine catalyst (PTC) to increase the cold conversion of hydrocarbons and carbon monoxide. Electric catalytic converters have also been proposed, wherein heating elements are arranged directly on or upstream of the exhaust aftertreatment devices.
The inventor herein has recognized potential issues with the above approaches. While post-injection can aid in raising exhaust-gas temperatures, post-injection of fuel is detrimental to overall fuel economy. Furthermore, combustion of fuel at low exhaust-gas temperatures leads to increased generation and deposition of soot or particulate matter, exacerbating fouling of exhaust aftertreatment devices. Furthermore, poor durability of pre-turbine catalysts has stunted their widespread introduction, and electric catalytic converters are too expensive and require too much power to be practical.
One approach that addresses the aforementioned issues is a method for reducing exhaust emissions from an internal combustion engine comprising powering a grid heater using an energy storage device to raise the exhaust-gas temperature during a first exhaust-gas condition, injecting fuel to raise the exhaust-gas temperature during a second exhaust-gas condition, and maintaining the exhaust-gas temperature by outputting power to the grid heater, injecting fuel, recycling the exhaust-gas, and cooling the recycled exhaust-gas with a cooler during a third exhaust-gas condition. Because the grid heater is used to heat the exhaust-gas entering the exhaust-gas aftertreatment device, the power requirements for the grid heater are much lower than those for electric catalytic converters, and as such, the grid heater can be installed without extensive modifications to existing energy supply sources. Another advantage is that the power supplied to the electrical grid heater may be generated by selective regenerative charging (SRC) technologies such as regenerative braking, thereby conserving fuel economy relative to conventional emissions discharge reduction methods. Furthermore, using a grid heater to heat the exhaust-gas flow during cold starts can prolong the life of exhaust-gas aftertreatment devices relative to post-injection methods because fuel injected when the exhaust-gas is cold results in higher soot deposition and fouling at the exhaust-gas aftertreatment device.
The above advantages as well as other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.